strange way to crash

I tried running the same query twice at the same time from a shell script:

#!/bin/bash
/usr/bin/time psql dbname uname -c 'select * from a_view where condition' &
/usr/bin/time psql dbname uname -c 'select * from a_view where condition' &


The system (linux) hangs after some time and the strange thing is that I can change between vconsoles with Alt+F[1-6]
butno other keyboard input goes through <!> hence I reboot. 

The query executes fine when ran by itself. Why should it crash if ran twice?

cheers,
thalis